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authorGrant Likely <grant.likely@secretlab.ca>2011-06-06 01:16:30 -0600
committerGrant Likely <grant.likely@secretlab.ca>2011-06-06 01:16:30 -0600
commitca632f556697d45d67ed5cada7cedf3ddfe0db4b (patch)
treef393534b929abb32813ea5c495f1ac6d93a10d1d /drivers/spi/spi-bitbang-txrx.h
parent8c99268431a117207a89be5167ecd69429fd4bda (diff)
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spi: reorganize drivers
Sort the SPI makefile and enforce the naming convention spi_*.c for spi drivers. This change also rolls the contents of atmel_spi.h into the .c file since there is only one user of that particular include file. v2: - Use 'spi-' prefix instead of 'spi_' to match what seems to be be the predominant pattern for subsystem prefixes. - Clean up filenames in Kconfig and header comment blocks Signed-off-by: Grant Likely <grant.likely@secretlab.ca> Acked-by: Wolfram Sang <w.sang@pengutronix.de> Acked-by: Linus Walleij <linus.walleij@linaro.org>
Diffstat (limited to 'drivers/spi/spi-bitbang-txrx.h')
-rw-r--r--drivers/spi/spi-bitbang-txrx.h97
1 files changed, 97 insertions, 0 deletions
diff --git a/drivers/spi/spi-bitbang-txrx.h b/drivers/spi/spi-bitbang-txrx.h
new file mode 100644
index 000000000000..c16bf853c3eb
--- /dev/null
+++ b/drivers/spi/spi-bitbang-txrx.h
@@ -0,0 +1,97 @@
+/*
+ * Mix this utility code with some glue code to get one of several types of
+ * simple SPI master driver. Two do polled word-at-a-time I/O:
+ *
+ * - GPIO/parport bitbangers. Provide chipselect() and txrx_word[](),
+ * expanding the per-word routines from the inline templates below.
+ *
+ * - Drivers for controllers resembling bare shift registers. Provide
+ * chipselect() and txrx_word[](), with custom setup()/cleanup() methods
+ * that use your controller's clock and chipselect registers.
+ *
+ * Some hardware works well with requests at spi_transfer scope:
+ *
+ * - Drivers leveraging smarter hardware, with fifos or DMA; or for half
+ * duplex (MicroWire) controllers. Provide chipselect() and txrx_bufs(),
+ * and custom setup()/cleanup() methods.
+ */
+
+/*
+ * The code that knows what GPIO pins do what should have declared four
+ * functions, ideally as inlines, before including this header:
+ *
+ * void setsck(struct spi_device *, int is_on);
+ * void setmosi(struct spi_device *, int is_on);
+ * int getmiso(struct spi_device *);
+ * void spidelay(unsigned);
+ *
+ * setsck()'s is_on parameter is a zero/nonzero boolean.
+ *
+ * setmosi()'s is_on parameter is a zero/nonzero boolean.
+ *
+ * getmiso() is required to return 0 or 1 only. Any other value is invalid
+ * and will result in improper operation.
+ *
+ * A non-inlined routine would call bitbang_txrx_*() routines. The
+ * main loop could easily compile down to a handful of instructions,
+ * especially if the delay is a NOP (to run at peak speed).
+ *
+ * Since this is software, the timings may not be exactly what your board's
+ * chips need ... there may be several reasons you'd need to tweak timings
+ * in these routines, not just make to make it faster or slower to match a
+ * particular CPU clock rate.
+ */
+
+static inline u32
+bitbang_txrx_be_cpha0(struct spi_device *spi,
+ unsigned nsecs, unsigned cpol, unsigned flags,
+ u32 word, u8 bits)
+{
+ /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
+
+ /* clock starts at inactive polarity */
+ for (word <<= (32 - bits); likely(bits); bits--) {
+
+ /* setup MSB (to slave) on trailing edge */
+ if ((flags & SPI_MASTER_NO_TX) == 0)
+ setmosi(spi, word & (1 << 31));
+ spidelay(nsecs); /* T(setup) */
+
+ setsck(spi, !cpol);
+ spidelay(nsecs);
+
+ /* sample MSB (from slave) on leading edge */
+ word <<= 1;
+ if ((flags & SPI_MASTER_NO_RX) == 0)
+ word |= getmiso(spi);
+ setsck(spi, cpol);
+ }
+ return word;
+}
+
+static inline u32
+bitbang_txrx_be_cpha1(struct spi_device *spi,
+ unsigned nsecs, unsigned cpol, unsigned flags,
+ u32 word, u8 bits)
+{
+ /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
+
+ /* clock starts at inactive polarity */
+ for (word <<= (32 - bits); likely(bits); bits--) {
+
+ /* setup MSB (to slave) on leading edge */
+ setsck(spi, !cpol);
+ if ((flags & SPI_MASTER_NO_TX) == 0)
+ setmosi(spi, word & (1 << 31));
+ spidelay(nsecs); /* T(setup) */
+
+ setsck(spi, cpol);
+ spidelay(nsecs);
+
+ /* sample MSB (from slave) on trailing edge */
+ word <<= 1;
+ if ((flags & SPI_MASTER_NO_RX) == 0)
+ word |= getmiso(spi);
+ }
+ return word;
+}